FIG. 14 is a cross-sectional view of a mounted multilayer ceramic capacitor 1.
The multilayer ceramic capacitor 1 includes a capacitor body 4 having a multilayer structure including a plurality of dielectric ceramic layers 2 and a plurality of internal electrodes 3a and 3b formed along a plurality of respective interfaces between the dielectric ceramic layers 2. The capacitor body 4 has a rectangular parallelepiped shape defined by first and second main surfaces 5 and 6 extending in a direction in which the dielectric ceramic layers 2 extend, first and second end surfaces 7 and 8 extending in a direction orthogonal to the first and second main surfaces 5 and 6, and first and second side surfaces (parallel to the plane of FIG. 14 but not shown in FIG. 14).
Although edges of a capacitor body are generally chamfered, the illustration of chamfered edges of the capacitor body 4 and those of other capacitor bodies is omitted in FIG. 14 and other drawings.
The multilayer ceramic capacitor 1 further includes first and second external electrodes 11 and 12 connected to the internal electrodes 3a and 3b, respectively, such that capacitances formed between the internal electrodes 3a and 3b facing each other with the dielectric ceramic layers 2 therebetween are extracted. The first and second external electrodes 11 and 12 are formed over the respective first and second end surfaces 7 and 8 of the capacitor body 4, and extend therefrom to respective parts of the main surfaces 5 and 6 and side surfaces adjacent to the end surfaces 7 and 8.
The multilayer ceramic capacitor 1 is mounted on a substrate 13 by bonding the first and second external electrodes 11 and 12 to the substrate 13 with a conductive bonding material 14, such as solder or a conductive adhesive, with the first main surface 5 of the capacitor body 4 facing the substrate 13.
A portion contributing to formation of capacitances between the internal electrodes 3a and 3b in the capacitor body 4 will be referred to hereinafter as the “active part”. In FIG. 14 illustrating the multilayer ceramic capacitor 1, an active part 15 is represented by a region surrounded by a dashed line. The active part 15 has a rectangular parallelepiped shape.
FIG. 15 illustrates the multilayer ceramic capacitor 1 in the same position as that in FIG. 14. In FIG. 15, the illustration of the internal electrodes 3a and 3b in the capacitor body 4 is omitted and only the active part 15 is illustrated.
When a voltage is applied across the first and second external electrodes 11 and 12 of the multilayer ceramic capacitor 1, dielectric polarization occurs at positions where adjacent internal electrodes 3a and 3b face each other. This makes it possible to obtain capacitances as described above. However, dielectrics provided by the dielectric ceramic layers 2 and located in the active part 15 cause electric-field-induced distortions depending on the applied voltage, as indicated by arrows 16 of FIG. 15. This causes the multilayer ceramic capacitor 1 to be deformed as indicated by dashed lines in FIG. 15.
When an alternating voltage is applied to the multilayer ceramic capacitor 1, deformation of the multilayer ceramic capacitor 1 resulting from electric-field-induced distortion causes the substrate 13 to vibrate and produces a sound called a “squeal”. A force that causes the substrate 13 to vibrate is also applied from parts of the external electrodes 11 and 12 located on the first main surface 5 of the capacitor body 4. When the level of “squeal” increases, a noise problem arises.
To suppress “squeal”, Japanese Unexamined Patent Application Publication No. 2000-281435 (Patent Document 1) proposes a technique in which a dielectric composition containing BaTiO3, SrZrO3 and CaZrO3 is used as the material of dielectric ceramic layers. This dielectric composition is highly resistant to reduction when baked and has a high dielectric constant, a low distortion factor, and good capacitance-temperature characteristics.
However, there are problems using the technique in which a distortion is suppressed by an improvement in material composition as described in Patent Document 1, in that it is difficult to achieve both a high dielectric constant and the like, and suppression of a distortion, and that the degree of design freedom is limited.
On the other hand, Japanese Unexamined Patent Application Publication No. 2004-39937 (Patent Document 2) proposes a configuration in which a ceramic base in a multilayer ceramic capacitor containing barium titanate as a dielectric material, except where there is an insulating gap, is covered with a metal film, include the terminal electrodes at both ends. The ceramic base is covered with the metal film such that the ratio of the surface area of a portion covered with the metal film to the entire surface area of the ceramic base is greater than or equal to 0.8. Since the surface of the ceramic base is mostly covered with the metal film, the ceramic base has a high stiffness, which makes it possible to suppress mechanical vibrations caused by electrostriction (electric-field-induced distortion).
However, the method of suppressing “squeal” described in Patent Document 2 has a problem in that the process of forming a metal film while maintaining a proper insulating gap is complicated.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-281435    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2004-39937